Systems and methods for direct current system digital carried message conveyance

ABSTRACT

The systems and methods of the present invention provide for conductive emissions communication without requiring dedicated communications wires. The systems and methods have the capability to send digital messages over the same wires that are used to power DC systems. Hardware filter circuits are combined with advanced algorithms in a communications control chip to permit the elimination of the dedicated wires, thereby needing zero additional wires to accomplish the task of digital control.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/611,235, filed 17 Sep. 2004, and entitled“Systems and Methods for Direct Current System Digital Carried MessageConveyance.”

FIELD OF THE INVENTION

This invention relates generally to digital communication systems. Inparticular, this invention relates to direct current conductiveemissions communications systems.

BACKGROUND OF THE INVENTION

Many forms of digital communications used today require separate wiresto carry the digital messages from one place to another. The onlyexception to this trend is RF (Radio Frequency) based systems. Systemsemploying RF technology transmit a radio signal through the air in thesame manner as a cellular phone.

When a non-RF system uses dedicated wires for communications, thosewires are often referred to collectively as the “communications bus.” Acommunications bus refers to a group of wires whose responsibility it isto get information from the source to the intended receiver or from thereceiver to the source. The reason that is done is to denote the factthat those wires are acting as a stand-alone sub-system and must beisolated from other sub-systems. In more complex systems it is possibleto have several communications buses. This would become necessary if thedifferent communications sub-systems were incompatible and the digitalinformation being conveyed by one sub-system would interfere with theoperation of another sub-system.

FIG. 1 is an illustration of a simple prior art communications bussystem that might be encountered in a mobile DC (Direct Current)application. This type of system is referred to as using conductedsignals or emissions. This means the signal itself is following aconductive path, e.g., a conductive wire of the communications bus. Thisresults in a more controlled message path, a message that can work atlow power levels and reduced chances of the signal interfering withother electronic devices.

Conducted emission systems to date have had one distinct disadvantage. Aconductive path can also carry many types of noise. This noise can comefrom many sources. Examples would be a motor, solenoid, generator orcertain types of lights. Radiated emissions of sufficient power can alsoattach themselves to a conductive path.

One prior art type of communications method that is gaining inpopularity is the Radio Frequency (RF) system, as shown in FIG. 2. Asexplained previously, this works in much the same manner as a cellularphone.

RF systems use what is referred to as a radiated transmission oremission. That type of signal is intentionally transmitted into the airsurrounding an antenna in all directions. Radiated emission devices aretightly controlled by the FCC (Federal Communications Commission) due totheir tendency to interfere with other electronic devices. ConventionalRF devices must transmit within well-defined ranges of frequencies thathave been established by the FCC. Most of the FCC frequencies require alicense to operate a transmitting device. There are specific frequenciesset aside for low power devices such as the ones used in the RF devicescurrently being discussed. These devices collectively are sometimesreferred to as “Part 15” devices as that is the section of the FCC rulesthey operate within.

To initiate a RF system, an input device receives information from apre-determined source. This could vary from a sensor monitoring acertain parameter to a switch sending a “go” or “stop” command. Once theincoming information is recognized, the input controller generates amessage for transmission. The input controller would then broadcast thatcoded message through the air to all other controllers in the system.One disadvantage to this scheme is that any electronic device capable ofreceiving air-born messages and in close proximity to the transmittingdevice would also receive the message.

In order to minimize the possibility of an unintended device respondingto an incoming message the originating controller would encode themessage with a special recognition number. To further reduce thepossibility of miscommunication, some systems employ what is referred toas a Spread Spectrum Frequency Hopping communications scheme. What thatmeans is that instead of broadcasting on only one frequency, thecontroller sends out portions of its message on different frequencies.The receiving device must be directed to know what frequency to start atand what other frequencies to hop to as the incoming message progresses.

The need remains for simplified digital communication systems andmethods that do not require dedicated communications wires and that senddigital messages over the same wires that are used to power DC systems.

SUMMARY OF THE INVENTION

It is an object of this invention to provide digital communicationsystems and methods that do not require dedicated communications wires.

It is also an object of this invention to provide systems and methodsthat send digital messages over the same wires that are used to power DCsystems, thereby eliminating the dedicated wires and requiring zeroadditional wires to accomplish the task of digital control.

These and other objects of the invention are achieved by providing acommunications system comprising an input device and an output device.The input device is coupled to a power source of the load power bus. Theoutput device is coupled to the input device and to a load by the loadpower bus and to the power source by a return power bus. The outputdevice comprises a filter, a receive detector, a controller, a transmitdriver, and a main processor.

The filter receives a command signal of a pre-determined frequencytransmitted by the input device over the load power bus and filterssignals that are not of the pre-determined frequency. The receivedetector receives signals from the filter and determines if the signalsmatch the pre-determined frequency and outputs a signal of thepre-determined frequency corresponding to the command. The controllerreceives the command from the receive detector and processes the commandin serial code. The transmit driver is located downstream of thecontroller and prepares messages received from the controller forinjection back into the load power bus. The main processor receives themessage from the controller.

According to one aspect of the invention, the system is a direct current(DC) system.

According to another aspect of the invention, the machine code comprisesa group of three Bytes.

Objects of the invention are also achieved by providing a conductiveemissions communications system comprising an input device, an outputdevice communicatively coupled to the input device by a power line, aload controlled by the output device, and means for transmitting acommand signal from the input device to the output device over the powerline without the use of a designated communications line. The outputdevice includes means for recognizing the command signal transmitted bythe input device, means for filtering interfering signals, and means forcontrolling the load based on the command signal without the interferingsignals.

According to one aspect of the invention, the system is a direct current(DC) system.

According to another aspect of the invention, the output device includesmeans for processing the command signal in serial code.

Objects of the invention are also achieved by a method of transmitting adigital communication comprising transmitting a command signal directlyover a power line from an input device, through an output device, and toa load without the use of a designated communications line. According toone aspect of the invention, the power line is part of a direct current(DC) system.

According to another aspect of the invention, the output device includesmeans for processing the command signal's serial code.

According to another aspect of the invention, interfering signals arefiltered from the command signal.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a prior art conductive emissionscommunications system having a dedicated communications bus fortransmitting a signal.

FIG. 2 is a schematic drawing of a prior art radio frequencycommunications system.

FIG. 3 is a schematic drawing of a conductive emissions communicationssystem that permits transmission of a command signal directly over apower bus.

FIG. 4 is a schematic drawing of a prior art automobile seat controlwiring system.

FIG. 5 is a schematic drawing of an automobile seat control wiringsystem using the system shown FIG. 3.

FIG. 6 is a schematic drawing of a prior art automobile mirror controlwiring system.

FIG. 7 is a schematic drawing of an automobile mirror control wiringsystem using the system shown FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention, which may be embodiedin other specific structures. While the preferred embodiment has beendescribed, the details may be changed without departing from theinvention.

It is useful for the purposes of this disclosure to have anunderstanding of terms commonly used in reference to communicationssystems.

Serial or Parallel refers to the way in which the information is sentout. In a parallel system, different parts of a message stream are sentover different wires. Computer printers to this day still use a parallelcommunications scheme. These types of systems can transmit at very highspeeds but require many more wires to accomplish the task. In a serialscheme, all of the data is sent out in one stream, one part of themessage stacked behind the other. This results in processing at slowerspeeds but using much fewer wires.

Baud rate is the same as the term bps (Bits Per Second). The term baudrate applies to an analog system (i.e., a modem or phone line basedsystem). The term bps refers to a digital system.

Twisted pair wires is a term used to describe a method of reducing theinfluence of external electrical noise on two wires. When you twist twowires together, the strength of the noise riding on the wires tends tobe lessened, or attenuated, where the lines cross each other. This is aless expensive way of trying to eliminate noise as opposed to shieldedcable. With shielded cable, a conductive foil wrap actually surroundsthe wires and is also wrapped over a bare conductor. The bare conductoracts as a drain for the foil shield when one of its ends is connected toground.

Synchronous is a term used to describe when a communications system iscontrolled by a timing clock. If the system is asynchronous a clock doesnot control it. The systems and methods of the present invention arepreferably synchronous.

Bi-directional means the system can send messages in both directions asopposed to uni-directional. The systems and methods of the presentinvention are preferably bi-directional.

Master-Slave or Peer to Peer. These two terms describe whether a systemhas one controller that is responsible for the control of acommunications system (Master-Slave) or if each controller (processor)can access the system (Peer to Peer).

I. System Overview

In reality all systems in use today, RF or otherwise, attempt to achievetwo things: 1) to reduce the number of wires required activating a loadof some sort; and 2) moving digital information.

An RF system uses a radio message transmitted from an input module totell a receiver output module what needs to be done or what informationis being passed. This in essence, replaces the dedicated communicationwires that used to run from the control device, such as a switch, to thecontrolled load or from one controller to another.

FIG. 3 illustrates a conductive emissions communications system 10 thatalso replaces those same wires and sends information, therebyeliminating the need for dedicated communication bus wires.

The system 10 includes a power source, e.g., a conventional directcurrent (DC) 12-volt battery 12. A load power bus 14 provides voltageand current from the battery 12 to an input device 16 (by way of aseries of switches 18), to an output device 20, and from the outputdevice 20 to one or more loads 22. By way of illustration, in anautomobile, a load 22 may take the form of a light, a motor, a horn, asolenoid, or any other component requiring activation and/ordeactivation. A return bus 24 provides voltage and power back to thebattery 12 from the output device 20.

Instead of transmitting a signal through the air like a RF system, thesystem 10 injects a message or transmitted command 26 directly onto theload power bus 14. That is, the power handling capability of the powerbus 14 is multiplexed in combination with signal transmission. The powerand return buses 14 and 24 define a two-conductor cable (e.g., black andred) system. Instead of a bundled harness for each command, only thepower 14 and return 24 cables are required. As only two cables need tobe checked/verified or replaced, troubleshooting and diagnostics aregreatly simplified.

As was discussed earlier, a conductive emissions communications systemis more apt to be affected by electrical noise from other devices. Onecommon type of noise is spurious frequency noise. Two different spuriousfrequency noises, denoted 28A and 28B to designate differentfrequencies, are shown in FIG. 3. Burst noise 30 is normally classifiedas non-cyclical momentary electrical voltage deviations (positive ornegative) and are often referred to as spikes.

The output device includes a filter 32, a receive detector 34, acontroller 36 (e.g., communications chip), a transmit driver 38, and amain processor 40, which communicate by way of a power line 42, whichrun in parallel to the power line 42, thus eliminating bulky seriesfilter elements. Together, these components enable the system 10 towithstand the burst 30 and spurious frequency noises 28A and 28Bnormally associated with low voltage DC systems.

A first group of cooperating components form the filter 32, which may beconnected via a capacitor to the power line 42. The filter 32 acts toblock signals that are not of a desired or proper frequency or thatotherwise do not match pre-determined criteria. The filter 32 ispreferably designed to work at a Center Frequency of 1.79 MHz. TheCenter Frequency is the midpoint of the range of frequencies, orbandwidth, that a filter will pass. This is equal to 1,790,000 Hertz orcycles per second. In a preferred embodiment, the filter 32 is anarrangement of various components commonly used in filter circuits andavailable from many manufacturers.

A second group of cooperating components form the receive detect network34. The network 34 monitors signals that have passed through the filter32 to determine if they match the desired frequency.

A third group of cooperating components form the transmit driver 38. Thedriver 38 prepares messages from the controller 36 for injection ontothe power line 42. In the illustrated and preferred embodiment, thedriver 38 is located on the downstream side of the controller 36. Afteran outgoing signal has passed through the controller 36, it is sent backthrough the filter 32 and onto the power line 14 as verification ofreceipt and transmission of the command signal 26.

The controller 36 contains the software that determines if the signalsent through the receive detector 34 is valid. If it is a valid signal,the information will be decoded and stored in a message buffer. The mainprocessor 40 is then notified that a new message has come in.

The controller 36 utilizes a communications processor chip along with aspecialized circuit board design that minimizes interference found inlow voltage DC circuits. In a preferred embodiment, the controller 36 isa very large-scale integration (VLSI) device, such as model QDC10available from Yamar Electronic, Ltd., of Tel Aviv, Israel.

The controller 36 and processor 40 use advanced algorithms to decode andprocess the command 26. All computers are nothing more than a group ofswitches. These switches can only be either on or off. That being thecase there are only two electrical voltage conditions that can exist,energized (Hi) or de-energized (Low).

This means that any computer or digital device must communicate in abinary language. A binary language has two characters to work with andthe characters are typically 0 (Electrically Low) or 1 (ElectricallyHi). No matter how complicated a device may be, it still works with asimple binary language. Binary language is also known as machine code.

Processors can only work with a fixed number of 1's and 0's at a time.For many years, processors used blocks of 8 characters of 1's or 0's. Anindividual 1 or 0 is called a Bit. A collection of 8 bits is called aByte, 4 bits is called a Half Byte. 16 bits is known as a Word and 32bits is referred to as a Double Word. In recent years, processors haveprogressed to the point where it possible to rapidly manipulate 16 bitsor 32 bits at a time.

Software in each independent electronic module communicates to othermodules in a typical system using synchronous (clocked) serial messages.The communications network is bi-directional (sends and receives) innature. Messages are constructed using a unique “group number” approach.One byte in each message is reserved for a group number. As all messagesare broadcast to every module in a system, the group number tells eachmodule if a particular message is meant for that module. The number alsopre-qualifies a message for internal processing by the intendedrecipient. The system format is a combination of Peer-to-Peer andMaster-Slave. As with a typical Peer-to-Peer system, each module cantransmit a message without direction from the Master. To help preventcollisions on the communications network, each module is assigned atransmit slot number. When a module has a message to send, it must waitfor its slot number to come up. The timing for the transmit slot iscontrolled by an internal timer built into each module. The Master pollsthe other modules in the system and can override any modules' command inthe event of a fault situation.

The illustrated system 10 uses a group of 3 Bytes or 24 Bits of binaryinformation.

Example of possible message of the systems and methods of the presentinvention: Byte 1 1 1 1 1 1 1 1 0 Prepare to transmit 3 Byte longmessage

Byte 2 0 0 0 0 0 0 1 0 Message is for Group 2 (On/Off function)

Byte 3 0 0 0 0 0 0 0 1 Turn “On” Group 2 function

The Group format method of message construction not only allows thesystems and methods of the present invention to transmit complexmessages with a minimum number of Bytes, it also allows for expansionand flexibility beyond the limitations of other message constructiontechniques.

When a message is sent out it has to have a specific target. Normally,this is accomplished by assigning a unique address to each potentialtarget. This is very limiting however, if one of the goals of the systemis to keep message length (total number of Bytes) to a minimum.

The Group format expands the capabilities of a single Byte ofinformation by accounting for the normally encountered redundancies inmost applications. Instead of assigning a specific address to eachtarget, groups are formed of targets that always respond together to aspecific command.

For example, in an automotive application, both headlights are normallyturned on or off at the same time. Instead of targeting a message toeach headlight, they can be grouped together so that one group commandcan operate both headlights. If an operator wishes to turn on only oneheadlight, the same group number can be used, but the command is changedto turn on only one headlight.

As another example, in many hydraulic applications it becomes necessaryto activate multiple valves simultaneously. An operator may use theGroup format and simply assign each valve grouping a separate groupnumber. If there were a particular valve that is a member of multiplegroups, then the processor output terminal for that valve would beassigned all of the group numbers required.

The software permits a variety of customized functions to be programmed.For example, lights can be programmed to be flashers or multiple motorsmay be simultaneously activated to allow a car seat to move forward andup at the same time with one switch. Customized safety features may alsobe programmed, e.g., to require a designated function or pass codebefore a switch can be activated. Diagnostics software greatlysimplifies troubleshooting. For example, diagnostic functions canmonitor loads and broadcast fault conditions to aid in diagnosing shortconditions.

If increased communication speed is necessary, an additional smallprocessor (not shown) may be provided to act as a buffer between thecommunications chip 36 and the main processor 40. The additionalprocessor would desirably monitor the communications chip 36, store newmessages, and transfer messages between the main processor 40 and thecommunications chip 36.

II. Use of the System

In use, an operator uses switches 18 to input a selected function intothe input device 16. The input device 16 transmits the command 26corresponding to the selected function onto the load power bus 14 fortransmission to the output device 20. The command 26 is a signaltransmitted as a pre-determined frequency or frequencies. As FIG. 3illustrates, frequency-based noises 28A/28B and burst noise 30 may alsobe present on the load power bus 14 along with the desired command 26 tothe controller 20 and thereby mask, disrupt, or otherwise interfere withthe command signal 26.

The filter 32 receives the command 26 as transmitted by the input device16 and filters interfering signals that are not of the pre-determinedfrequency. The filter 32 then transmits the “filtered” signals to thereceive detector 34. In some cases, the filter 32 may not be able toremove all interfering noises. For example, FIG. 3 illustrates asituation in which the filter 32 has removed the burst noise 30 andfrequency-based noise 28B. However, the filtered signals still retainfrequency-based noise 28A along with the command signal 26.

The receive detector 34 receives the signals from the filter 32 anddetermines if the signals match the pre-determined frequencycorresponding to the command signal 26. In the illustrated example, thereceive detector 34 recognizes that the noise 28B does not correspond toany pre-determined frequency and disregards the noise signal 28B. Thereceive detector also recognizes the command signal 26 as correspondingto a pre-determined frequency and outputs the command 26 to thecontroller 36.

The controller 36 receives the command 26 from the receive detector 34and decodes and processes the command 26 in binary language comprising aGroup of three Bytes, as previously described. The controller 36 thentransmits the confirmed message to the main processor 40.

III. Representative Applications

One of the significant features of the systems and methods of thepresent invention is the relative ease of custom configuration forvaried applications in multiple markets. The systems and methods of thepresent invention are built on a modular design platform so manyapplications can be accomplished with minimal development time. Thesystem 10 is inherently reliable through the utilization of commonlyused components.

Automotive:

Mainstream: At the time of manufacturing, vehicles may be equipped bythe manufacturer with individual controls and indicators for securitysystems, interior & exterior lights, sound & video systems, climatecontrol, and various options available on the vehicle.

Aftermarket: Available in standard modules, customers (e.g., car rebuildshops, actual end-users) may purchase the modules they need for theirspecific requirements. Modules would be designed to interface withaftermarket “kits” so that features like electric windows, securitysystems and custom lighting could be easily added to older vehicles.Modules would also interface with aftermarket or original equipmentmonitoring and control systems.

FIGS. 4 and 5 are illustrative embodiments of automobile seat controlwiring. FIG. 4 illustrates a conventional prior art system employing amultiplicity of additional dedicated wires. FIG. 5 illustrates use ofthe system 10 of the present invention to eliminate the need forinterconnecting load control wires. In the embodiment illustrated inFIG. 5, the control module serves as the output device 20 and the doorpanel control center serves as the input device 16. The system 10 mayalso be interfaced with DVD, Stereo/Radio, and security systems.

FIGS. 6 and 7 are illustrative embodiments of automobile mirror controlwiring. FIG. 6 illustrates a conventional prior art system employing amultiplicity of additional dedicated wires. FIG. 7 illustrates use ofthe system 10 of the present invention to eliminate the need forinterconnecting load wires. The control module serves as the outputdevice 20 and the mirror control center serves as the input device 16.

Specialty Truck:

Municipal: Switch inputs, indicators, and joysticks for controlling snowplows, salt spreaders, augers, lift mechanisms, and specialty lightingincluding strobes & emergency lights may be installed. The advantagesover existing systems are: reduced installation time, significantlysmaller in size (cab space), simplified trouble shooting, increasedcontrol capability, and improved performance.

Forestry Equipment:

Logging: The described systems and methods are well-suited forinstallation on vehicles and equipment used in processing lumber andlog-handling. The typical wire harnesses used to operate the variousmechanisms are very complex and can be difficult to troubleshoot. Thesystems and methods of the present invention reduce cost, simplifywiring requirements, improve system reliability, and increase operatorcontrol.

Agriculture:

The systems and methods of the present invention can be used to controlthe application of fertilizers and weed control liquids, hydraulics,pneumatics, pumps, seed dispensing equipment, and crop harvestingdevices. With simplified wiring systems, equipment dealers can installthe systems and methods of the present invention at the factory or atthe dealership. Troubleshooting is greatly simplified with primarycheckpoints at the controls and the modules.

Redundant System Applications:

The systems and methods of the present invention can be installed inaddition to existing systems and used as a primary or backup inapplications such as:

Aviation:

The simplicity and size (weight) of the systems and methods of thepresent invention provide a primary or backup electrical system forcontrols and indicators. By connecting to the system bus, the systemsand methods of the present invention can be installed with existingsystems and utilized as necessary. The reliability and lightweightcomponents of the systems and methods of the present invention providedistinct advantages over conventional systems.

Recreational Vehicles:

As the complexity of a recreational vehicle's electrical systemincreases, the need to reduce wire harness weight and assembly timebecomes more acute. The systems and methods of the present invention areideally suited to help accomplish these goals. One example would be theuse of multiple control panels connected to a power bus running thelength of the vehicle. Interior lights and other devices controlled atthe front of the vehicle could also be controlled at other locations inthe vehicle requiring only the two wires in the power bus.

Marine:

Boats need to be as lightweight as possible to increase top endperformance, reduce fuel consumption and increase cargo capacity. If aboat is loaded with features, the systems and methods of the presentinvention could reduce the number of interconnecting wires by 40% ormore. The use of software to mimic complicated switch or relay controlscan reduce the overall part count and total system cost.

Mobile Equipment:

Cranes, bulldozers, road graders, and other pieces of equipment that uselarge banks of electro-hydraulic valves could benefit from a lesscomplex wire harness.

The foregoing is considered as illustrative only of the principles ofthe invention. Furthermore, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and operation shown anddescribed. While the preferred embodiment has been described, thedetails may be changed without departing from the invention.

1. A communications system comprising a. an input device coupled to apower source by a load power bus, and b. an output device coupled to theinput device and to a load by the load power bus and to the power sourceby a return power bus, the output device comprising i. a filter forreceiving a command signal of a pre-determined frequency transmitted bythe input device over the load power bus and filtering signals that arenot of the pre-determined frequency, ii. a receive detector forreceiving signals from the filter and determining if the signals matchthe pre-determined frequency and outputting a signal of thepre-determined frequency corresponding to the command, iii. a controllerfor receiving the command from the receive detector to filter out thecommand and, iv. a transmit driver downstream of the controller toprepare messages received from a main processor for injection back intothe load power bus, and v. the main processor for communicativelyreceiving and sending said messages with said controller.
 2. Acommunications system as in claim 1 wherein the system is a directcurrent (DC) system.
 3. A communications system as in claim 1 whereinthe message comprises a serial message comprising a group of threeBytes.
 4. A communications system as in claim 3 wherein one of the Bytesindicates that a message is to be transmitted.
 5. A communicationssystem as in claim 3 wherein one of the Bytes identifies a group oftargets to receive a message.
 6. A communications system as in claim 3wherein one of the Bytes corresponds to a designated command function.7. A communications system as in claim 1 wherein said controllerreceives harmonic frequencies from the receive detector using softwarealgorithms to filter out the command and construct a binary serialmessage for said controller.
 8. A conductive emissions communicationssystem comprising an input device, an output device communicativelycoupled to the input device by a power line, a load controlled by theoutput device, and means for transmitting a command signal from theinput device to the output device over the power line without the use ofa designated communications line, the output device including means forrecognizing the command signal transmitted by the input device, meansfor filtering interfering signals, and means for transmitting thecommand signal to an output device processor without the interferingsignals.
 9. A conductive emissions communications system as in claim 8wherein the system is a direct current (DC) system.
 10. A conductiveemissions communications system as in claim 8, wherein the output deviceincludes means for processing the command signal, said command signalcomprising a serial message.
 11. A conductive emissions communicationssystem as in claim 10, wherein the serial message comprises a group ofthree Bytes.
 12. A conductive emissions communications system as inclaim 11, wherein one of the Bytes indicates that a message is to betransmitted.
 13. A conductive emissions communications system as inclaim 11 wherein one of the Bytes identifies a group of targets toreceive a message.
 14. A conductive emissions communications system asin claim 11 wherein one of the Bytes corresponds to a designated commandfunction.
 15. A method of transmitting a digital communicationcomprising transmitting a command signal directly over a power line froman input device, through an output device, and to a load without the useof a designated communications line.
 16. A method as in claim 15 whereinthe power line is part of a direct current (DC) system.
 17. A method asin claim 15, further comprising processing the command signal, thecommand signal comprising a binary serial signal.
 18. A method as inclaim 15, further comprising filtering interfering signals from thecommand signal.
 19. A communications system as in claim 17 wherein theserial message comprises a group of three Bytes.
 20. A communicationssystem as in claim 19 wherein one of the Bytes indicates that a messageis to be transmitted.
 21. A communications system as in claim 19 whereinone of the Bytes identifies a group of targets to receive a message. 22.A communications system as in claim 19 wherein one of the Bytescorresponds to a designated command function.